Reflectometry endeavors to solve measurement problems with solutions that involve considerable sophistication. An existing problem is a need to devise reflectometers, or optical systems, that lend themselves to a more accurate measurement of diffuse reflectance than has been attained to date This problem is recognized in a paper authored by Keith A Snail, entitled "New Optical Systems for the Measurement of Diffuse Reflectance," in a book entitled "Infrared, Adaptive, and Synthetic Aperture Optical Systems," R. Barry Johnson, William L Wolfe, Janet S Fender, Editors, Proc , SPIE 643, page numbers 84-92 (1986), published not before 13 Oct. 1986 Several solutions to this problem have been devised that form the substance of the invention. Specific solutions to the problem are set forth in the above-referenced paper by Keith A. Snail This paper is hereby incorporated by reference into this patent application. These and other solutions will be described with reference to several specific embodiments of the invention.